The easter gene encodes a protein that is homologous to the trypsin family of serine proteases and is involved in the proper patterning of the Drosophila embryonic dorsal-ventral (D-V) axis. I am studying easter's role in Drosophila dorsal-ventral patterning. To do this, I have produced Easter protein recombinantly in Drosophila Schneider S-2 cells. This protein has been tested both in vitro and in vivo for activity, and is functional. I have established that Easter is a protease and that its substrate seems to be the protein spaetzle, a protein known to function downstream of Easter in the same pathway. Our attention is now focused on understanding how Easter's proteolytic activity is controlled spatially. By determining Easter's extended substrate specificity and using the Computer Graphics Laboratory facilities, we hope to design a specific inhibitor of Easter to monitor its activity in vivo. Secondly, we use the wealth of genetic knowledge on Easter, the expressed Easter proteins with mutations that are known to cause mutant phenotypes. As well as characterizing these proteins biochemically, we use visualization tools to model these mutant proteins and to gain insight into how these mutations might physically perturb the protein to cause the mutant phenotypes. The use of CGL greatly enhances our knowledge of D-V patterning in Drosophila.